Something major to consider is that the fit of a 52cm between one manfuacturer is often different (and sometimes very different) than a 52cm between another manufacturer. The key is to look at the bike geometry, especially the top tube tength, and gauge it from there. If you have the ability, even do a bike fitting at a local shop. With the right equipment, they can suggest what frame size is optimal for you, and can also suggest stem length, handlebar width, etc. that will make the best fit.